The objective of the proposed research is to obtain and to make use of suitable mutants to analyze developmental pathway control and pattern formation in the ciliate Tetrahymena pyriformis. (1) High- and low-temperature sensitive mutations affecting cell division, cell shape, and surface pattern formation will continue to be selected, genetically analyzed, and combined with one another to analyze sequences of expression of gene products. Mutations will also be selected that specificially affect expression of the recently discovered transformation to a "rapid swimmer" phenotype and that modulate expression of a new mutation, psm (pseudomacrostome) that brings about a radical switch in developmental pathways. (2) Modifications of positioning of contractile vacuole pores and oral structures that arise as direct or indirect consequences of mutations will be analyzed with the aid of suitable measurements. A mutation (disl) that brings about considerable disorganization of ciliary meridians without apparent influence on positioning of the new oral apparatus will also be morphometrically analyzed. (3) 180 degrees inversions of ciliary meridians have recently been obtained in T. pyriformis; an attempt will be made to generate such inversions on the specific ciliary meridian along which the new oral apparatus develops in order to find out the degree to which that meridian controls the polarity and asymmetry of oral development. (4) The expression of psm will be subjected to detailed study, including subjection to various types of physiological perturbations, in an attempt to elucidate the control of pathway selection and oral organelle positioning, both of which are disturbed in this mutant (which in some ways resembles homoeotic mutants of Drosophila). An attempt will be made to counteract expression of psm using breis of wild type cells.